@article{10_4064_cm_44_2_291_299,
     author = {Aleksander Ca{\l}ka},
     title = {Curvature of lift spaces},
     journal = {Colloquium Mathematicum},
     pages = {291--299},
     publisher = {mathdoc},
     volume = {44},
     number = {2},
     year = {1981},
     doi = {10.4064/cm-44-2-291-299},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm-44-2-291-299/}
}